This invention relates generally to the field of natural gas production, transportation, and processing. In one aspect, this invention relates to a method of removing oxygen from natural gas. In another aspect, this invention relates to an apparatus for removing oxygen from natural gas.
Natural gas is one of the most popular forms of energy today. It is used for heating, cooling, production of electricity, and it finds many uses in industry. Natural gas is produced, sometimes along with oil, by drilling into the earth""s crust to locate subterranean deposits of natural gas. In most natural gas fields, the subterranean natural gas deposits are under sufficient pressure that the natural gas will flow freely to the earth""s surface. In some older natural gas fields, however, a lifting system is required to extract natural gas from the subterranean formation.
One common problem associated with the production of natural gas is the presence of oxygen in natural gas. Typically, oxygen enters the natural gas via air leaks in the production or transportation system. Air leaks are primarily a problem in the portions of the system where natural gas is maintained at less than atmospheric pressure. When a lifting system is required to draw the natural gas out of the ground, the natural gas located between the subterranean natural gas deposit and the initial pipeline booster compressor typically has a pressure which is less than atomospheric pressure. In these subatmospheric pressure regions, air is naturally drawn into the system through even the smallest of openings due to the pressure differential between the conduit carrying the natural gas and the atmosphere.
Although oxygen typically enters natural gas near the upstream production and transportation end of the system, the negative impacts of oxygen in natural gas are apparent throughout the midstream and downstream transportation and processing regions. Problems associated with the presence of oxygen in natural gas include the following: (1) oxygen contributes substantially to the corrosion of piping used to transport the natural gas from the gathering wells to the gas plant, (2) during regeneration of molecular sieves at the gas plant, oxygen reacts with hydrocarbons and hydrocarbon residues to produce char which plugs and coats the molecular sieves, thereby reducing the life of the molecular sieves, (3) oxygen contributes to the deterioration of amine fluids used in the gas plant to remove acid gasses from the natural gas stream, and the salts generated as a result eventually precipitate or cause foaming in the treaters of the gas plant, and (4) purchasers of natural gas recognize the problems associated with the presence of oxygen in natural gas and, therefore, impose a penalty on the price they will pay for gas containing excessive amounts of oxygen.
In the past, operators of natural gas facilities have attempted to lower oxygen levels in natural gas by seeking out and repairing air leaks in the production and transportation systems. However, even with these preventative measures, oxygen levels of greater than 50 ppmv (parts per million by volume) in natural gas are common.
It is therefore an object of the present invention to provide a system for removing oxygen from natural gas.
A further object of the present invention is to provide a system for removing oxygen from natural gas which does not require expensive reactors, separators, chemicals, and/or catalysts.
A still further object of the present invention is to provide a system which converts the oxygen in natural gas into a marketable compound which is easily separable from natural gas.
Additional objects and advantages of the invention will be apparent in the description which follows and the appended claims.
In accordance with an embodiment of the present invention, a method for removing oxygen from natural gas is provided. The method comprises contacting a volume of oxygen-containing natural gas with nitric oxide under conditions sufficient to produce nitrogen dioxide.
In accordance with another embodiment of the present invention, an apparatus for removing oxygen from natural gas is provided. The apparatus comprises a natural gas line for transporting natural gas, a nitric oxide source, and a nitric oxide injector fluidically coupled to the natural gas line and the nitric oxide source. The nitric oxide injector is operable to conduct nitric oxide from the nitric oxide source into the natural gas line.
The present invention provides a simple and economical system for the in-line removal of oxygen from natural gas. The by-products of the inventive system are marketable compounds which are easily separable from natural gas.